This invention is generally concerned with apparatus for feeding sheets from a stack of sheets and, more particularly, for feeding respective sheets one at a time from the bottom of an upright stack of sheets on a deck, including means for compensating for variations in forces exerted on the respective sheets by the stack and deck as the respective sheets are fed from the stack.
U.S. Pat. No. 3,977,668 for DUAL PURPOSE SHEET MATERIAL FEEDING AND SAFETY APPARATUS, issued Aug. 31, 1976 to Bologna, et al. and assigned to the assignee of the present invention, discloses an upright stack of sheets which is supported on a feed deck inclined at an angle relative to an upright wall for urging an edge of each of the sheets into registration with the wall. In addition, there is disclosed opposed output feed rollers situated at the junction between the deck and wall for feeding respective sheets one at a time from the bottom of the stack.
U.S. Pat. No. 4,973,037 for a FRONT END FEEDER FOR MAIL HANDLING MACHINE, issued Nov. 27, 1990 to Holbrook and assigned to the assignee of the present invention, discloses sheet feeding apparatus comparable to the apparatus shown in the aforesaid '668 patent, for use in a high speed machine for handling mixed mail pieces, wherein a drive assembly is provided for feeding successive mailpieces from the bottom of the stack of sheets while maintaining the mailpieces in registration with a fence and fluffing the stack to promote separation of the respective mailpieces from one and other.
When the aforesaid sheet feeding apparatus and like structures are utilized for separating large envelopes or other sheets, the individual sheets may weigh so much that the frictional forces exerted by the stack and deck against the drive forces exerted by the feed rollers are such that the respective sheets either cannot be fed from the stack or are misfed therefrom. This ordinarily occurs in due to the forces exerted by the feed rollers being insufficient to overcome the static frictional forces exerted by the deck and stack on the lowermost sheet of the stack, or, as a given sheet is exiting the stack, due to the normal force exerted by the stack on the given sheet being insufficient to permit the opposed outfeed roller to frictionally engage and feed the sheet from beneath the stack. In any event, any given sheet being fed from the bottom of a stack is subjected to a wide range of normal forces in the course of being fed therefrom. Accordingly,
an object of the invention is to provide an apparatus for feeding respective sheets from a stack thereof including means for compensating for variations in forces exerted on the respective sheets in the course of feeding the same; PA1 another object is to provide such compensating means including a microcomputer programmed for intermittently driving respective rollers engaging the lowermost sheet of the stack to ensure separation of the sheets and feeding the sheets from the stack; and PA1 another object is to provide structure for controlling a plurality of sheet feeding rollers, engaging successive lowermost sheets of the stack, in consideration of the length of such sheets in the direction of feeding.